The overall goal of the proposed research is to study the conformational changes that nucleosomes undergo as functions of solution conditions. In addition to CD and ultracentrifugation three fluorescence methods will be used: steady-state fluorescence anisotropy, fluorescence intensity decay, and decay of fluorescence anisotropy. These are highly sensitive to conformational changes. Various fluorescence probes will be used. Among these are N-(3-pyrene)-maleimide (NPM) bound to the sulfhydryls of the H3 molecules of the core protein, intrinic tyrosine of histones, and ethidium bromide (EB) intercalated into the DNA of the nucleosome. When bound to core protein, NPM fluorescence is unusually sensitive to conformational changes due to the formation of excimers between two pyrene moieties. The long-term goal is to understand the various conformational changes that nucleosomes can assume, since it is known that nucleosomes change as a result of gene activation and may also change during other cellular processes.